Wireless communication systems keep evolving to meet the needs for providing continuous and faster access to a data network. In order to meet these needs, wireless communication systems may use multiple carriers for the transmission of data. A wireless communication system that uses multiple carriers for the transmission of data may be referred to as a multi-carrier system. The use of multiple carriers is expanding in both cellular and non-cellular wireless systems.
A multi-carrier system may increase the bandwidth available in a wireless communication system according to a multiple of how many carriers are made available. For instance, a dual-carrier system may double the bandwidth when compared to a single carrier system and a tri-carrier system will triple the bandwidth when compared to a single carrier system. In addition to this throughput gain, diversity and joint scheduling gains may also be expected. This may result in improving the quality of service (QoS) for end users. Further, the use of multiple carriers may be used in combination with multiple-input multiple-output (MIMO).
By way of example, in the context of third generation partnership project (3GPP) systems, a new feature called dual-cell high speed downlink packet access (DC-HSDPA) has been introduced in release 8 (R8) of the 3GPP specifications. With DC-HSDPA, a base station communicates to a wireless transmit/receive unit (WTRU) over two downlink carriers simultaneously. Besides doubling the bandwidth and the peak data rate available to WTRUs, but also has a potential to increase the network efficiency by means of fast scheduling and fast channel feedback over two carriers.
For DC-HSDPA operation, each WTRU is assigned two downlink carriers: an anchor carrier and a supplementary carrier. The anchor carrier carries all physical layer dedicated and shared control channels associated with transport channels such as the high speed downlink shared channel (HS-DSCH), the enhanced dedicated channel (E-DCH), and the dedicated channel (DCH) operations. Such physical layer channels include, by way of example, the fractional dedicated physical channel (F-DPCH), the E-DCH hybrid automatic repeat request (HARQ) indicator channel (E-HICH), the E-DCH relative grant channel (E-RGCH), the E-DCH absolute grant channel (E-AGCH), the common pilot channel (CPICH), the high speed shared control channel (HS-SCCH), and the high speed physical downlink shared channel (HS-PDSCH)). The supplementary carrier may carry a CPICH, an HS-SCCH and an HS-PDSCH for the WTRU. The uplink transmission remains on a single carrier in the current system. The high speed dedicated physical control channel (HS-DPCCH) feedback information is provided on the uplink carrier to the Node-B and contains information for each downlink carrier.
It has been proposed to extend this feature to non-adjacent downlink (DL) carriers, (e.g., carriers in different frequency bands). It has also been proposed to extend the dual-cell concept to the uplink. Thus, the WTRU may transmit on two carriers and receive on two carriers.
In wideband code division multiple access (WCDMA) and HSPA, a WTRU monitors link quality by estimating the DL dedicated physical control channel (DPCCH) or F-DPCH quality, and by monitoring the cyclic redundancy check (CRC) on the dedicated physical data channel (DPDCH), if configured. The physical layer reports in-synch and out-of-synch indications to a radio resource control (RRC) layer in the WTRU in accordance with a particular criteria. The RRC layer processes the in-synch and out-of-synch indications and may determine that radio link failure has occurred. More specifically, if the RRC in the WTRU receives a predefined number (e.g., N313) of out-of-synch indications, the WTRU starts a predetermined timer (e.g., T315). If the WTRU does not receive a predefined number (e.g., N315) of in-synch indications before the predetermined timer expires, a radio link failure is declared.
When dual-cell (or multi-cell) operation is implemented with carriers in different frequency bands, there is a significant probability that the link quality is considerably different between the two bands. For example, if the WTRU moves indoors, and the indoor penetration characteristics are better in one of the two bands, it is possible that the radio link may be maintained in one of the two bands. When this situation arises, it is not clear how the WTRU should behave to minimize disruption of its connection to the network. There currently exists no mechanism to handle radio link failure in the context of multiple carriers.
Therefore, there exists a need for an improved method for radio link establishment and monitoring.